Predictability in the evolution of Orthopteran cardenolide insensitivity

Area of Science:

• Evolutionary biology
• Molecular evolution
• Insect-plant interactions

Background:

• Cardenolides are plant toxins inhibiting Na+,K+-ATPase (ATPα) in insects.
• Distantly related insects repeatedly evolve insensitivity to cardenolides, a striking example of parallel adaptation.
• Previous studies identified parallel amino acid substitutions and gene duplication/neo-functionalization in five insect orders.

Purpose of the Study:

• To investigate cardenolide insensitivity evolution in a sixth insect order, Orthoptera (grasshoppers).
• To expand the taxonomic scope for understanding parallel evolution of ATPα insensitivity.
• To identify specific molecular sites and evolutionary mechanisms driving this adaptation.

Main Methods:

• Comparative genomic analysis of ATPα in Pyrgomorphidae grasshoppers (Orthoptera).
• Analysis of amino acid substitutions at key ATPα sites.
• Examination of gene duplication and neo-functionalization events.

Main Results:

• Orthopterans exhibit predictable patterns of ATPα evolution for cardenolide insensitivity, consistent with other insect orders.
• Negative pleiotropic constraints appear to be a key determinant in this evolutionary process.
• Positive selection acts on specific ATPα sites (111, 115, 118, 122) depending on gene copy number.

Conclusions:

• The evolution of cardenolide insensitivity in insects is a highly convergent process.
• Negative pleiotropic constraints and positive selection on specific ATPα sites are major drivers.
• Findings support a unified model for insect adaptation to cardenolide-rich plants across diverse lineages.